Sensitized electrophotographic layers

ABSTRACT

This invention relates to the optical sensitization with styryl dyes of electrophotographic materials, preferably containing zinc oxide as the photoconductor.

States Patent nin piei" ei ai,

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[ SENSITIZED lELiECTROPHOTOGRAPHIC LAYERS Helmut Kampler; Hansihlschliiger, both of Cologne, Starnmheim; Woli Gmiericii, Leverkusen,all of Germany AGFA-Gevaert Akflengeseilschmfi, Leverkusen, GermanyFiled: May 18, 1966 Appl. No.: 551,033

Inventors:

Assignee:

Foreign Application Priority Dam May 29, 1965 Germany ..A 49348 us. an..96/i.7, 260/2409 1m. rzi. ..G03g 5/08 lFieidoliSem-eh ..96/l.6,1.7,89,102, 106;

[56] Reierences Cited UNITED STATES PATENTS 2,393,743 1/1946 Brooker eta1. ..260/240.9 X

Primary Examiner-Charles E. Van Horn Attorney-Connolly and Hutz ABSTRACTThis invention relates to the optical sensitization with styryl dyes ofelectrophotographic materials, preferably containing zinc oxide as thephotoconductor.

6 Claims, 7 Drawing Figures PATENTEU JAN] 81972 HELMUT KAMPFEP, HANSOHLscHLAcER,

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INVENTORS.- WOLF GES/ER/CH.

A TTOEN E YS SENSl'lllZElD ELECTROPll-IOTOGRAPHIC LAYERS It is alreadyknown that photoconductive layers whose inherent sensitivity isgenerally in the ultraviolet region of the spectnim, can be sensitizedwith respect to visible light by the addition of dyes capable oftransmitting radiant energy. The dyes which have been proposed for thispurpose are members of a variety of groups for example, triphenylmethanedyes, phenolsulphone phthaleins, xanthene and acridine dyes, andcyanines, merocyanines and oxonoles belonging to the polymethine groupof dyes.

Unfortunately, the known dyes have the disadvantage that either theyproduce an inadequate increase in sensitivity, or else they color theelectrophotographic layer to an extent beyond the acceptable limit. ingeneral, however, it is only possible to use colorless or practicallycolorless layers. The second of these two disadvantages is particularlytroublesome in the case of electrophotographic materials because thesensitizing dyes used cannot be washed out by the usual methods oreliminated by baths. Removal of the sensitizing dyes by bleachingfollowing production of the image is complicated and is economicallyunfavorable.

The object of the invention is to develop optically sensitizedelectrophotographic layers which preferably contain zinc oxide as thephotoconductor, are as color free as possible and whose sensitivityremains unaffected by storage. It has now been found that dyescorresponding to the general formula Ri CN \N- VCH=C/ 12 R4 areeminently suitable for sensitizing electrophotographic layers,preferably zinc oxide layers, where:

R, and R represent hydrogen; alkyl with preferably up to 20 carbonatoms, more particularly an alkyl with up to eight carbon atoms, thealkyl radicals being optionally substituted by carboxyl, esterifiedcarboxyl, in particular with aliphatic alcohols with up to 20 carbonatoms, esterified carboxy, carbonamide, alkyl-substituted carbonamide,nitrile, halogen such as chlorine or bromine, thiocarbonamide,alkyl-substituted thiocarbonamide, hydroxyl, alkoxy with preferably upto 12 carbon atoms, amino, alkyl-substituted amino with preferably up to12 carbon atoms, phenyl, sulpho, sulphonamide, alkyl-substitutedsulphonamide, and sulphonic acid ester groups; aryl, preferably phenylor naphthyl, in which case the phenyl rings may be substituted byhydroxy, alkoxy, preferably with up to l2 carbon atoms, alkyl withpreferably up to l2 carbon atoms, halogen such as chlorine or bromine,sulphonic acid, and carboxy groups or R and R together with theirlinking nitrogen atom may represent a fiveor six-membered heterocyclicring.

R represents hydrogen, alkyl with preferably up to live carbon atoms,halogen such as chlorine or bromine, nitro, or nitrile or R and Rtogether may represent the ring members required to complete aheterocyclic fiveor six-membered ring fused to the ring in the formula.

R represents nitrile or an acyl group, is. radicals derived from anorganic carboxylic or sulphonic acid, for example alkyl-sulphonyl withup to 20 carbon atoms, arylsulphonyls, preferably phenylornaphthylsulphonyl which, if desired, may be substituted, carboalkoxywith alkyl radical containing up to 20 carbon atoms, carboaryloxy,preferably carbophenoxy, amino-carbonyl whose amino group may besubstituted by alkyl with up to 20 carbon atoms, aryl such as phenyl ornaphthyl, or heterocyclic groups such as benzthiazolyl, thiadiazolyl andbenzthiazolyl-phenyl, the amino group may optionally be substituted byacyl radicals derived from preferably short-chain aliphatic carboxylicacids,

or from carbonic acid, carbamic acids and thiocarbamic acids, or may bea member of a five or six-membered heterocyclic ring for examplepyrrolidine; aminothiocarbonyl which may also be substituted asdescribed above, hydrazinocarbonyl, optionally with the substitutentsmentioned immediately above, as well as acyl groups derived fromaliphatic or aromatic carboxylic acids, for example, benzoyl, acetyl,stearoyl, and propionyl. R. may in addition represent carboxyl,sulphonic acid or sulphonic acid esters, in particular with aliphaticalcohols; the radicals represented by R, may in turn by furthersubstituted by nitrile, hydroxyl, mercapto, alkoxy, or carboalkoxygroups.

The compounds listed in the following tables have proved to beparticularly suitable:

TABLE I Ra R1\ TI 2 /CN /N 1 0H=0\ R1 Rt N0. R1 Ra a B4 1 M.P., C. 1 CHCH; H 22mm SOQCHQ CH:COOH CH2COOH H --C0OCH3 1 214-216 -CH2COOH -CH2C0OHH -coNHcH1c0oCHi 181-182 -CH2COOH CH3 H -c0NHi 198-201 -CH2C0OH -0H1o0oHH --CN l 214-216 CH3 CH3 H -cN 182-184 H; -CH2COOH H -CN 1 191-193CHzCH1CN -CH2CH2CN H -CN 226-228 H H3 3-CH5 -CN 205-207 0H1 -CH GHzCO0HH -0N 1 149-152 CH; CH; B-NO; -CN 152-154 CH5 CH1 3-01 -oN 207 CH3 OH; H4300011; 127-129 CH3 -CHCOOH H o0ocH1 I 129-131 15, cm -CH2CO0II 1r 1232-234 IH- cm mm on.I m, -onn1mcN minimums: 1| cooom wins 11.. n z:i-om uoocm ism-20a 18.. CH; "CII2C1'I2COOII l -COOCH3 ll2-ll5 111.. on,cm s-nr -co0cm 88-94 20. c1ocH2c1 1t -CO0CH; 123-121;

Table l(ontinued No. R1 R: R; R M.P., C.

(53.. C113 (Jlz(3()()li ll N-HUm,. 221 225 ()Nil LS/ 64 -CIIzCOOIIC112COOil H N' I l 201-4203 C()NII S/ ml tlilztlUUll (Uncool; It 11842-c -NHC 0.111..

I i'illl'litiiitltititii.

TA ll m, H 20 The cyanacetamides used are obtained from cyanoaceticester (lihiIUUll l N a 'lllt Nll. it. M.l

I. -UONlh l'lpnrldiuesalt196-200(J. 2... (IN Yiporldlno salt 173-177 (J.3 C00Cli3 Plperldine salt. 152-154 C.

The dyes according to the invention are prepared as known per se bycondensing the corresponding aldehydes with active cyanomethylcompounds. Condensation may be carried out by heating the componentseither in the presence or in the absence of solvents, optionally in thepresence of acidic or basic condensation agents, as illustrated in thefollowing examples.

COMPOUND 1 Three grams of p'dimethylamino benzaldehyde are heated for 5minutes with 4 g. of cyanomethyl-p-tolyl sulphone in 50 ml. of ethanolin the presence of 3 ml. of piperidine. Following recrystallization fromacetone, 4.] g. of dye No. l in table 1 melting at 220 to 224 C., areobtained in the form of orangered needles.

COMPOUND 2 Five grams of p-aminobenzaldehyde-N,N-diacetic acid arerefluxed for minutes with 2 g. of methyl cyanoacetate and 3.6 g. ofpiperidine in ml. of ethanol. On cooling, dye No. 2 in table 1 isprecipated as the piperidine salt in the form of yellow needles.Following recrystallization from alcohol, 4.8 g. of the dye areobtained, m.p. 214 to 216 C.

COMPOUND 3 2.2 g. of l,2,3,4-tetrahydroquinoline-6-aldehyde-l-aceticacid and 1.0 g. of cyanacetamide are boiled for 10 minutes with 3 ml. ofpiperidine in ml. of ethanol. Following isolation and recrystallizationfrom isopropanol, 3 g. of dye No. l in table 2 are obtained in the formof the piperidine salt, m.p. 196 to 200 C.

COMPOUND 4 and the corresponding amines, or from cyanoacetic acid andthe amines in acetic anhydride, while the cyanthioacetamides can beprepared from the cyanacetamides by sulphuration with P 8 and thecyanmethyl sulphones prepared from the corresponding sulphonic acids andchloroacetonitrilc.

'I'he dyes according to the invention sensitize an electrnphotographiclayer in the blue region of the spectrum with sensitization maximabetween 420 and 480 m/u. 'lhese dyes are distinguished by their narrowsensitization range with a steep slope in the sensitization curvetowards the long-wave region. This, coupled with their highsensitization intensity make them eminently suitable for the bluesensitization of electrophotographic materials, for example colormaterials or other materials processed under copying light with aconsiderable blue component. Another advantage of the dyes ac cording tothe invention is the hardly noticeable coloring of the image layers.

The sensitizers according to the invention are added to the layers insuch quantities that each square meter of the completed photoconductinglayer contains from 0.] to 10 mg. sensitizer. In general,electrophotographic layers are sensitized by grinding the photoconductorpigment with a solution of the sensitizing dye in a suitable solvent,for example methyl or ethyl alcohol, followed by evaporation of thesolvent. As a result, the sensitizing dye is deposited on the surface ofthe photoconductor pigment grains. The pigment may then be processedwith a lacquer binding medium to form the electrophotographic layer asknown per se. The dyes according to the invention may be applied withequal success by other sensitizing processes. One of these processes,for example, comprises adding a solution of the sensitizing dye in aliquid inert with respect to the binder, to the photoconductor/bindermixture before dispersion. A further alternative, which has theadvantage of yielding electtophotogtaphie layers with hardly anycoloring, is embodied in the sensitizing process described in BritishPatent Specification No. 919,684. Finally, the sensitivity of acompleted, nonsensitized photoconductor-binder layer may be displacedinto the longer wave region of the visible spectrum by subsequentlydipping it into a solution of the sensitizing dye, following by drying.The reference to these alternatives is intended to emphasize that theuse of the sensitizing dyes according to the invention is not limited toany specific method of processing.

Neither isthe use of the dyes according to the invention limited tospecific photoconductor/binder systems. Suitable photoconductors forsystems such as these include, above all, the inorganic and organiccompoundswhich, by virtue of their natural coloring, do not show asensitivity peak in the sensitizing range of the styryl dyes, i.e., forexample zinc oxide, titanium dioxide or arsenic trioxide and, on theother hand, organic compounds such as anthracene, and phenanthrene.Suitable vehicle for the process according to the invention include inprinciple all the film formers used in electrophotography for examplesilicone resins, alkyd resins, polyurethanes or polyvinyl acetate.

EXAMPLE I Ten milligrams of dye No. 10 in table I are dissolved in 100ml. of methyl alcohol. The solution is added to and thoroughly mixedwith I g. of a photoconductive zinc oxide powder. The solvent is thenremoved by evaporation at 65 C. To prepare the electrophotographiclayer, the zinc oxide thus colored is dispersed in a mixer with 45 ml.of a 60 percent by weight solution of a phenylmethylpolysiloxane resinin toluene, the resulting dispersion is coated on to a baryta papersupport and then dried. After it has been charged, the resultingelectrophotographic materials is exposed to form an image and developedby a conventional developing process using a toner powder or a liquidaerosol. An excellent reproduction of the original is obtained.

EXAMPLE 2 A ZnO layer is prepared by the procedure described in exampleI In this'case, dye No. 10 is replaced by dye No. 3 from table 2.Similar results are obtained when dyes 45, 43, 47, and 35 from table Iare used.

The spectral sensitivity of the zinc oxide layers prepared as describedin the preceding examples is illustrated in the accompanying FIGS. 1 to7.

FIG. I shows the spectral sensitivity curve of a nonsensitized zincoxide layer.

FIG. 2 illustrates the sensitization properties of the material preparedas described in example I, while FIGS. 3 to 7 relate to thephotoconductive layers prepared as described in example 2 using dye Nos.3 (FIG. 3), 45 (FIG. 4), 43 (FIG. 5), 47 (FIG. 6) and 35 (FIG. 7).

The sensitization curves were obtained as follows: the layer to beexamined is exposed with 4,000 Lux. see. from an imageenlarging lamp(RADIUM R 226, 230v./250 w.) through an interference sky filter, VERIL B60, a product of Messrs. Schotten and Genossen.

The filter is covered by a transparent grey step wedge so that a curvepath appears in the photoconductive layer as the developable image. Thepath is reproduced in the accompanying Figures in the form of a linedrawing. The height of the ordinates of the maximum of thissensitization curve enables the effectiveness of the sensitizing dye tobe assessed, while the abcissae enable the position of the sensitizationmaximum in the visible range of the spectrum to be determined.

In every case, the electroaerosol process described in British PatentSpecification No. 944,645 was used to make the filter exposures visible.

The photoconductive materials according to the invention may be used forany type of electrophotographic process, for example for developingprocess in which a solid, dustlike toner powder is used, for aerosoldeveloping processes, electrophoretic processes or for so-calledwetting-type developing processes. The materials according to theinvention are suitable both for processes in which electrostatic chargedimages are processed, and for processes in which conduction images areprocessed.

We claim: 7 I

l. A photosensitive electrophotographic material comprising at least onephotoconductive material consisting of zinc oxide dispersed in a binderand a sensitizing dye contained in the photoconductive material in theamount of 0.1 to 10 mg. per square meter of sensitizing dye, thesensitizing dye being of the formula l CONHCHzCOOCzH5 --CH2COOII 2. Aphotosensitive electrophotographic material comprising at least onephotoconductive material consisting of zinc oxide dispersed in a binderand a sensitizing dye contained in the photoconductive material in theamount of 0.1 to I0 mg. per square meter of sensitizing dye, thesensitizing dye being of the formula I N CH=C CN momooon 3. Aphotosensitive electrophotographic material comprising at least onephotoconductive material consisting of zinc oxide dispersed in a binderand a sensitizing dye contained in the photoconductive material in theamount of 0.l to 10 mg. per square meter of sensitizing dye, thesensitizing dye being of the formula Cg: /CN

CH3 CONHCSNH2 4. A photosensitive electrophotographic materialcomprising at least one photoconductive material consisting of zincoxide dispersed in a binder and a sensitizing dye contained in thephotoconductive material in the amount of 0.1 to 10 mg. per square meterof sensitizing dye, the sensitizing dye being of the formula -CH1C O CHCN N -CH=C o ONHz 5. A photosensitive electrophotographic materialcomprising at least one photoconductive material consisting of zincoxide dispersed in a binder and a sensitizing dye contained in thephotoconductive material in the amount of 0.1 to 10 mg. per square meterof sensitizing dye, the sensitizing dye being of the formula C ONHC OCH:

2. A photosensitive electrophotographic material comprising at least onephotoconductive material consisting of zinc oxide dispersed in a binderand a sensitizing dye contained in the photoconductive material in theamount of 0.1 to 10 mg. per square meter of sensitizing dye, thesensitizing dye being of the formula
 3. A photosensitiveelectrophotographic material comprising at least one photoconductivematerial consisting of zinc oxide dispersed in a binder and asensitizing dye contained in the photoconductive material in the amountof 0.1 to 10 mg. per square meter of sensitizing dye, the sensitizingdye being of the formula
 4. A photosensitive electrophotographicmaterial comprising at least one photoconductive material consisting ofzinc oxide dispersed in a binder and a sensitizing dye contained in thephotoconductive material in the amount of 0.1 to 10 mg. per square meterof sensitizing dye, the sensitizing dye being of the formula
 5. Aphotosensitive electrophotographic material comprising at least onephotoconductive material consisting of zinc oxide disperseD in a binderand a sensitizing dye contained in the photoconductive material in theamount of 0.1 to 10 mg. per square meter of sensitizing dye, thesensitizing dye being of the formula
 6. A photosensitiveelectrophotographic material comprising at least one photoconductivematerial consisting of zinc oxide dispersed in a binder and asensitizing dye contained in the photoconductive material in the amountof 0.1 to 10 mg. per square meter of sensitizing dye, the sensitizingdye being of the formula